Socket and plug connection for electric circuits



Feb. 23, 1960 F. METELLI 2,926,327

SOCKET AND PLUG CONNECTION FOR ELECTRIC CIRCUITS Filed Feb. 4, 1957 2 Sheets-Sheet 1 IN VEN TOR.

Feb. 23, 1960 F. METELLI 2,926,327

SOCKET AND PLUG CONNECTION FOR ELECTRIC CIRCUITS Fgllgd Feb. 4, 1957 2 Sheets-Sheet 2 IN V EN TOR.

BY 7 M11 1 M4 aaI 2,926,327 Patented Feb. 23, 1960 SOCKET AND PLUG CONNECTION FOR ELECTRIC CIRCUITS Francesco Metelli, Milan, Italy, assignor to Italo Rizzieri, Milan, Italy 7 Application February 4, 1957, Serial No. 638,070

Claims priority, application Italy February 3, 1956 1 Claim. (Cl. 339-41) Thisinvention relates to an electrical outlet socketplug arrangement, and more particularly relates to a new and improved electrical outlet of the type which includes a socket having metallic contacts adapted for connection to a source of electrical supply. Alternating current or direct current may be supplied to the metallic socket contacts so that an electrical potential will exist between the contacts. The plug is adapted to be connected by suitable cables to an electrically operated apparatus or device.

Connection between the contacts of the socket and the contacts of the plug is made by a two step operation. The first step comprises insertion of the plug into the corresponding opening of the socket. The second step comprises the turning of the inserted plug in the socket.

It is an object of this invention to provide a novel construction of an electrical outlet socket-plug arrangement of the type referred to, wherein the contacts located in the socket, between which an electrical potential exists, are 'completely shielded so that no electrical connection can'be made with the contacts either accidentally or deliberately by any other object except the plugs, once this plug is withdrawn from the opening in the socket.

It is a further object of this invention to provide a construction of an electrical outlet socket-plug arrangement wherein an infant will not be able to connect the contacts of the socket so as to receive an electrical shock or cause a Short circuit in the socket by thrusting a finger of a metallic object, for example a screw driver, a pair of scissors, or other narrow metallic elements into the electric socket opening designed for the insertion of the plug.

""It is a further object of this invention to provide a construction of an electrical outlet socket-plug arrangement which will prevent the withdrawal of the plug from the opening in the socket unless the plug has previously been turned into a position in which the connection between the contacts of the socket and plug is broken.

- It is a further object of this invention to provide an electrical outlet socket-plug arrangement in which the plug is locked in the socket in the electrical contact making position so that the plug cannot be withdrawn from the opening in the socket in axial direction when the electrical connection is made between the contacts of the socket and the contacts of the plug.

It is a further object of this invention to provide an electrical outlet socket-plug arrangement in which electrical connection between the contacts of the socket and the contacts of the plug can be made only after the inward movement of the plug into the opening of the socket is completed.

'With the above objects in view, an electrical outlet socket-plug arrangement according to the present invention includes a socket having a substantially cylindrical recess therein and a stationary cover with a substantially cylindrical opening coaxial with the recess and having a diameter smaller than the recess, the cover being formed with a plurality of angularly spaced slots extendirig in" radial directiono'utwardlytrom the opening, a

plug having a plurality of angularly spaced contact elements extending in radial direction therefrom, the plug being insertable through the opening in the cover with a a contact element passing through the slots therein into the I recess of the socket into inserting position and being turnable therein from the inserting position into a contact making position in which the plug cannot be removed from the socket without turning back into the insertion position. Also provided are a plurality of contact members mounted in the recess of the socket in spaced angular relationship and adapted to engage the contact elements on the plug when the same is in contact making position, a plurality of springs respectively engaging the contact members of the socket and tending to move the contact members in radial direction into tight contact with the contact elements of the plug when the latter is in contact making position and a hollow cylindrical insulating element coaxially arranged in the cylindrical recess of the socket and supported therein turnably about its axis, the insulating element being formed with a plurality of angularly spaced slots extending in radial direction through the walls of the hollow cylindrical insulating element. The insulating element is turnable between an insulating position in which the insulating element covers the contact members and in which the slots in the insulating element are aligned with the slots 'in the cover so that the contact elements of the plug may be inserted through the slots in the cover into the slots of the insulating element and a contact exposing position in which the slots in the insulating element are aligned with the contact members so that the springs can press the contact members into contact with the contact elements of the plug.

According to another feature of this invention, the contact elements and the contact members are metallic and the plug covers fully the opening in the socket when the plug is inserted into the opening thereof so that the contact members are fully shielded.

The invention itself, both as to its construction and its method of operation, together with additional objects and advantages thereof will be best understood from the following description of the specific embodiments when read in connection with the accompanying drawings in which:

Figure l is a partly cross-sectional side elevational view taken along line 1-1 of Figure 3, with the plug spaced from the socket,

Figure 2 is a partly cross-sectional side elevational view taken along line 22 of Figure 4, with the plug inserted and turned into the contact making position,

Figure 3 is a transversal sectional fragmentary view of the socket of Figure 1 taken along the line 3-3 of Figure 1,

Figure 4 is a transversal sectional fragmentary view of the socket of Figure 2 taken along lines 4-4 of Figure 2,

Figures 5, 6 and 7 are partly sectional side views of modified details of the socket shown in Figures 1, 2 and 4,

Figure 8 is a partly cross-sectional side view of a modified embodiment of the present invention,

' Figure 9 is a partly cross-sectional side view of embodiment illustrated in Figure 8 in the contact making position, and

Figures 10 and 11 are transversal cross-sectional fragmentary views of Figure 8 along lines 9-8 and 101tl, respectively.

In the drawings the same reference numerals indicate the same parts throughout the several figures.

.Referring to Figures 1 to 4, the plug, constructed in accordance to the current knowledge of the art, includes a male cylindrical portion 20 of insulating material such 3 r, portion '21. Terminals (not shown) to which the cable conductors'are connected, are enclosed in handle portion 21. The plug has a plurality of angularly spaced contact elements 22 extending in radial direction therefrom near the lower end of male portion 20. A three-pole plug is shown in Figure l by Way of example.

The socket includes a stationary cover 23 including a neck portion 24. A substantially cylindrical opening is formed in the neck portion of the cover and is dimensioned to allow the passage of male cylindrical portion 29 of the plug. The cover is formed with a plurality of angularly spaced slots 25 extending in radial direction outwardly from the opening in the' cover.

Coaxially with the opening of the stationary cover there is formed in the cover also a substantially cylindrical recess, the diameter of the opening being smaller than the diameter of the recess.

A hollow cylindrical insulating element 27 is arranged coaxially in the cylindrical recess of the socket and is supported therein turnably about its axis. The insulating elements 27 are formed on its upstanding side wall 28 with a plurality of angularly spaced slots 29 extending in radial directions through the walls of the hollow cylindrical insulating element. Slots 29 are dimensioned and arranged so that the contact elements 22 of the plug can pass therethrough when slots 25 are aligned with slots 29.

A number of contact members 26 are mounted in the socket and are angularly portioned in relation to the slots 25 so that the contact elements 22 can not engage contact members 26 when the plug is inserted in the socket, until the plug is turned in the socket after its insertion.

The hollow cylindrical insulating element 27 with its upstanding side walls 28, in which the slots 29 are formed, is turnable to an insulating position in which the walls 28 of the insulating element cover the contact members 26 and in which the slots in the insulating element are aligned with the slots 25 in the neck portion 24 so-that the contact elements 22 of the plug 20.can pass therethrough. When the plug is inserted into the socket contact elements 22 will pass through slots 25 and 29. The position of the slots 25 and 29 for this operation is illustrated in Figure l. The contact elements 22 will pass into a plane parallel to line 3-3 of Figure 1 and to line 44 of Figure 2. The second step of operation comprises turning of the plug in the socket to bring contact elements 22 into engagement with contact members 26 of the socket so that the electrical circuit is closed. It will be observed that such turning movement and therefore closing of the electrical circuit can occur only when the main portion 20 of the plug is fully inserted into the socket because only after full insertion can the plug be turned in the socket into the contact making position.

The turning movement of the arrangement illustrated in the drawing will be through an arc of 60 since three contacts are provided. A turning movement over an arc of 90 will be made, if only two contacts are provided in the arrangement.

Each contact member 26 is urged by a spring into contact with the contact element 22. Contact members 26 are urged by the springs in radial direction into tight contact with the contact elements 22 when the latter are in the contact making position.

When the plug is in the contact making position, that is when each contact element 22 is in contact with contact members 26, contact elements 22 are located offset angularly in respect to slots 25. Therefore, the plug cannot be withdrawn from the socket, since contact elements 22 are out of alignment with the slot 25 and the opening in the cover is too small to let the contact elements pass through except through the slots 25. Withdrawal is only possible after the plug has been turned 4 so that it carries the insulating element into its insulating position.

A turning movement of the plug Will result also in a turning inovement'of the hollow cylindrical insulating element 27 since contact elements 22 are located in slots 29. The insulating element 27 is thus turnable between an insulating position in which the walls 28 of the insulating element 27 cover and shield the contact members 26 and in which the slots 29 are aligned with the slots 25 of the neck portion 24 so that the contact elements 22 of the plug can be inserted through the slots 25 into the slots 29 of the insulating element 27 and a contact exposing position in which the slots 29 of the insulating element 27 are aligned with the contact members 26 so that'the springs behind the contact members 26 can press the contact members 26 into contact with the contact elements 22 of the plug.

In Figure 1 the plug is shown spaced from the socket, in Figure 2 the plug is shown inserted and with the insulating element 27 turned into the contact exposing position.

Several modifications of the hollow cylindrical insulating element 27 are shown in Figures 5 to 7 In Figure 5 the cup-shaped hollow cylindrical insulating element is provided with a frusto conical extension 30 at the bottom of the element in order to improve its bearing during rotation in the socket.

The cylindrical insulating element of Figure 6 is provided at the circumference thereof With a flange 31 to improve its axial mounting in the socket. A flange will however, not improve the angular mounting of the insulating element in the socket.

The hollow cylindrical insulating element of Figure 7 is not in the form of a cup as illustrated in Figures 1 to 6 but is in the form of a tube provided again with a flange 31 for retention in the socket. Such an insulating element is particularly useful in the case where an auxiliary axial contact is desired, for example where a connection through the base has to be made.

A modified embodiment of an electrical outlet socketplug arrangement is illustrated in Figures 8 to 11. The plug has contact elements in the form of parallel metallic pins 40, two being shown as an example. Pins 40 can be inserted into an insulating element 42 rotatably mounted in the socket 41. Insulating element 42 has a cylindrical portion turnably mounted in a recess of the socket defined by contact members 26'.

Insulating element 42 is provided with slots 43 through which pins 40 can pass. Preferably, the insulating ele-' ment 42 is made integral with an outer disc-like portion 44 located at the front face of socket 4-1. Disc-like portion 44 is provided with slots 45 (see Figure 8) arranged for the passage of pins 40. The plug is shown turned through an arc of from the position in which the pins 40 can be inserted in the plug. The insulating position of the insulating element 42 is illustrated in Figure 8 while the contact exposing position of the same is illustrated in Figure 9. Contact members 26' are spring urged into close contact with the contact elements 40 of the plug when the plug is inserted and turned into the contact exposing position.

Socket 41 is provided with an inwardly facing flange portion 46 adapted to slide into and engage grooves 47 formed in the pins 40 so as to lock the plug in the socket when the cylindrical insulatingelement is in the contact exposing position. Details of the flange 46 incorporated in the embodiment of Figures 8 to 11 is illustrated in greater detail in Figure 10. Flange portion 46 has at its inner periphery formed two grooves 48 arranged for the passage of the pins 40 therethrough. The two grooves 48 are offset in respect to the socket contact member 26' so that the plug can be inserted into the socket and can be withdrawn therefrom.

The position of the turnable insulating element 42 iii-its insulating position is shown in Figure 10. The posi arrangement according to the present invention gives novel and unexpected advantages since it provides means for completely and safely shielding the contact members of the socket so that the contact members can not be exposed and no contact can be made in an unauthorized manner, say by inserting a finger or any metallic part, except by the contact elements of the plug after the two specific steps of insertion and turning of the plug have been performed. v

The present invention also provides a simplified con- An'electrical outlet socket-plug arrangement comprising, in combination, a socket having a substantially cylinstruction of an electrical outlet socket plug arrangement which can be manufactured from a small number of simple;

drical recess therein and a stationary cover with a substantially cylindrical opening coaxial with said recess and hava ing a diameter smaller than said recess, said cover being formed with a plurality of angularly spaced slots extending in radial direction outwardly from said opening; a plug having a plurality of angularly spaced contact elements extending .in radial direction therefrom, said plug being insertable through the opening in said cover with said contact elements passing through said slots therein into said recess in said socket into inserting position and being turnable therein from said inserting position into a contact-making position in which said plug cannot be removed from said socket withoutturning back into said inserting position; a plurality of contact members mounted in said recess of said socket in spaced angular relationship and adapted to engage the contact elements on said plug when the same is in contact-making position; a plurality of springs respectively engaging said contact members and tending to move said contact members in radial direction into tight contact with said contact elements of said plug when the latter is in contact-making position; and a hollow cylindrical insulating element polyethylene so that the hollow cylindrical insulating ele-,

ment will not be damaged when the springs urge the contacting elements against the outer periphery of the cylin-- drical insulating element. The outer periphery of the hollow cylindrical insulatingtelement is dimensioned so that it is resiliently urged against the various parts of the socket which contact this outer periphery'so that the cylindrical insulating element will be-held in any given position by the friction and will not be easily turnable in the socket and is ready for repeated insertion and withdrawal of the plug from the socket through the slots therein.

It will be understood that each of the features described above or any combination thereof may also find a useful application in other types of electrical outlets socket-plug arrangements difiering from the form of embodiment described above.

reveal the gist ofthe invention that others can, by ap plying current knowledge, readily adapt it for various Without further analysis, the foregoing will ,so fully applications without omitting features that, from the stand-' point of prior art, fairly constitute essential characteristics of the generic and specific aspects of this invention and coaxially arranged in said cylindrical recess of said socket and supported therein turnable about its axis, said insulating element being formed with a plurality of angularly spaced slots extending in radial direction through the walls of said hollow cylindrical insulating element, said insulating element being turnable between an insulating position in which said insulating element covers said cont-act members and in which the slots in -said insulating element are aligned with said slots in said cover so that the contact elements of said plug may be inserted through said slots in said'cover into said slots insaid insulating element, and a contact-exposing position in which said slots in said insulating element are aligned with said contact members so that said springs can press said contact members into'contact with said contact elements on said plug.

References Cited in the file of this patent UNITED STATES PATENTS Great Britain July 12, 

